In conventional magnetoresistive memory architectures, writing individual memory cells without also writing adjacent or other non-intended cells is a problem. Typically, writing a magnetic tunnel junction (MTJ) memory cell involves passing electrical currents simultaneously through a bit line (generally defined along a y axis) and a word line (generally defined along an x axis) at the intersection of which the intended MTJ cell resides. Thus, selected cells in a thin film magnetic random access memory (MRAM) are written by the coincidence of x-oriented and y-oriented magnetic fields. The selected MTJ cell will experience a magnetic field which is the vector sum of the magnetic fields created by the word and bit line currents. All other MTJ cells that share the same bit line or word line as the selected MTJ cell will be half-selected and thus will be subjected to either bit line or word line magnetic fields, respectively.
Certain factors, such as variations in the geometry (e.g., shape or size) of an MTJ cell, can give rise to variations in magnetic switching thresholds of the MTJ cells which are so large that it is virtually impossible to write a selected cell without also inadvertently switching some of the half-selected cells, thus placing the reliability and validity of the stored data in question. Increasing the thickness of layers within the cell can reduce, in part, some of the effects of these variations. However, an increase in thickness effects the switching properties of the cell, i.e., coercivity, such that the switching fields of the cell become inoperably large.
Therefore, magnetic memory devices are needed wherein the unwanted switching of half-selected cells is minimized or eliminated, while desired switching properties are retained.